I. Field of the Invention
The present invention relates to implantable devices used to stimulate the heart to control the heart""s rhythm. This invention is more specifically directed toward leads used to connect a pulse generator to the left side of the heart to provide defibrillating pulses to the heart.
II. Description of the Prior Art
As set forth in U.S. Pat. No. 5,803,928 granted on Sep. 8, 1998 to Tockman et al, important health benefits can be derived by positioning an electrode in a branch of the great vein of the heart to treat tachycardia. Others have discussed positioning an electrode in the vasculature of the left side of the heart to treat heart failure. The present invention contemplates placing an electrode there for purposes of defibrillation.
Not all leads are suitable for placement in the vasculature of the left side of the heart. Many leads have too great a diameter, are too inflexible, and include structures that do not permit the lead to be safely and easily advanced through the vasculature. Such problems are compounded when the lead must also be suitable for delivery of defibrillation pulses.
As indicated above, it is often advantageous to defibrillation therapy to the left ventricle of the heart. While it is possible to secure a defibrillation electrode to the exterior of the left ventricle, doing so involves cracking the chest wall and other highly invasive and traumatic surgical protocols. Much of this surgical trauma can be avoided through the use of a transvenous lead. Placing the lead in the left ventricle can increase the potential for clotting. Clear advantages can, therefore, be derived by placing the electrode in a branch of the coronary vein. However, for such a lead to be successfully implanted in this fashion for effective delivery of therapy to the ventricle, it must be of a design capable of meeting six critical needs.
First, such a lead must be designed so that one or more of its electrodes can be positioned in one of the coronary veins of the left side of the heart. As such, the distal end of the lead must follow a path which includes the right atrium, the coronary sinus and one of the coronary veins.
Second, the lead must include a suitable shocking electrode. To be suitable, the shocking electrode must be of a proper length, be sufficiently supported for both placement and explant, and yet flexible enough to travel through the venous structure.
Third, the lead must have an electrode capable of pacing and sensing. This may be accomplished using the same electrode used for shocking. Alternatively, separate electrodes on the lead can be used to perform the pacing and sensing functions.
Fourth, proper fixation of the lead is key. Once the electrode is properly positioned, it must remain in that position indefinitely. Changes in position can be caused by a variety of factors, including blood flow, if the lead is not properly fixed in place.
Fifth, if an xe2x80x9cover-the-wirexe2x80x9d type design is used, the open end of the lumen could be sealed once the guidewire is withdrawn. Otherwise undesirable flow of blood through the lumen of the lead might occur.
Finally, the terminal pins of the lead must be properly sized. They must be sized for coupling to the defibrillator. They also must permit removal of a guide catheter.
Leads constructed in accordance with the subject invention meet each of these six critical criteria through the incorporation of various specifically designed structures. First, leads of the present invention have a proximal section possessing adequate axial stiffness for torquing and pushing purposes. Such leads also have a flexible distal section for traversing the required path. The outer surface is coated with a lubricious material for ease of insertion. The tip is designed to be atraumatic to heart and vascular tissue. The lead is also designed to cooperate with a guidewire during the implantation process.
Second, the defibrillation electrode is sufficiently supported for placement and explant. The electrode is also properly sized and sufficiently flexible to travel through the venous structure. Once implanted, the electrode is capable of delivering adequate defibrillation pulses to the heart.
Third, sensing or pacing is performed either using the same electrode which delivers defibrillation pulses to the heart, or a separate electrode. If a separate electrode is used, it must have characteristics similar to the defibrillation electrode as discussed above and the lead body structure should have individually insulated conductive elements.
Fourth, any fixation device used to assure that the electrode is maintained in the proper position is designed to not interfere with efforts to place the electrode in the proper position. Thus, rather than impacting the cross-section of the lead during implantation, the fixation device either (a) biases in the lead body""s conductive coil; (b) comprises one or more dissolvable polymers in the lead body to permit fibrotic attachment to the vein wall; or (c) has deployable tines. The fixation mechanism may also be made detachable to allow for explant of the lead.
Fifth, a guidewire will typically need to be used to position the electrode properly. If the lead has a distal opening and is passed over the guidewire, the distal opening is sealed once the electrode is properly positioned. In accordance with the present invention, this can be accomplished through the use of either a silicone flap, a hydrophilic material which swells upon fluid contact to close the distal opening, or the use of a deployable plug.
Finally, the terminal pins of the lead are designed to accommodate removal of a guide catheter. Either the terminal pins must be made small enough or the terminal pins must be removable.
More specifically, the present invention provides a lead suitable for both delivery of defibrillation pulses and placement in the vasculature of the heart. In one embodiment, a single lumen lead is provided. This lead includes an electrically conductive single open-lumen inner conductor coil comprising a winding of multiple wires to reduce electrical resistance. The coil is covered with an insulative material such as silicone, polytetrafluoroethylene (PTFE) or polyurethane. The proximal end is equipped with a terminal connector that can be plugged into the pulse generator. Just distal of the terminal connector is a self-sealing disk that permits passage of a guidewire and seals upon removal of the guidewire. Near the distal end of the lead are one or more electrodes specifically designed for flexibility and delivery of defibrillation pulses. The distal end, itself, includes a tip designed to be atraumatic and to dilate the venous structures to facilitate lead implantation. The lead may also include a fixation device for retaining the lead in the proper position.
Other embodiments of the invention provide a multi-lumen lead having one or more conductive cables passing through the lumens and attached to one or more electrodes. Again, a terminal connector for each cable, a self-sealing disk and an atraumatic tip are provided.
Further information related to the present invention and the advantages it offers can be derived from a review of the following detailed description of the invention in conjunction with the drawings which are a part of this specification. The specification is not intended to be limiting. Instead, the scope of the invention is defined by the claims when interpreted broadly to include a full range of equivalents.